While cleaning (once is not usual) my workshop, I fell on some slates of the Monts d’Arrée, full of rust. And as I had a little time, I took the smallest of them to try an engraving and I chose a knotwork pattern from the book of Kells.
The top layer of the slate has left in places, removing the rust color on fragments of the pattern but I’m not too dissatisfied with the result.